The present invention relates to an electrode system and method for cathodically protecting metal objects against corrosion. More particularly, this invention relates to electrodes of zinc, aluminum, magnesium, platinum, platinum-coated titanium, which are magnetically and electrically secured to ferro-magnetic metals, such as steel, steel compounds, nickel, cobalt for cathodically protecting these metals against corrosion.
Sacrificial anodes are used in various metal structures, for example, hot water heater tanks, water tanks, and ship's hulls, in order to prevent corrosion of the metal structure. Metal surfaces, particularly those of ferrous materials, when exposed to air and water, undergo oxidation or corrosion. While metal surfaces may be coated (for example, with zinc) or lined (for example, lining the interior of a hot water tank with glass), such coatings and linings are subject to imperfections or breakage and are frequently expensive. As such, many manufacturers use sacrificial anodes of a galvanically active metal, such as zinc, aluminum or magnesium, instead of such coatings and linings, or in addition to them as extra protection against corrosion. In such cathodic protection systems, the anode is both physically and electrically attached to the surface. The anode becomes depleted during its operational life to provide cathodic protection to the surrounding metal structure (i.e., the inside of the tank or the hull of a ship) and must eventually be replaced.
The cathodic protection of ferro-magnetic metals by means of electrodes is well known in the prior art. For example, U.S. Pat. No. 3,513,082, issued to Beer et al., discloses an anode attached to a magnet, which in turn is attached by magnetic action to the surface to be protected. The magnetic provides the physical attachment of the device to the surface as well as electrical conductivity between the anode and the surface.
There are a number of advantages to this attachment method. By securing the sacrificial anode to the object by means of a metal magnet, the replacement and/or renewal of the sacrificial anode and of the metal magnet is a simple operation. Furthermore, it is not necessary to provide special fastening means for the magnet since the magnet itself provides secure contact. Attachment of sacrificial anodes by use of magnetism may be convenient various small vehicles, tools, and other items of normal, everyday use.
However, such an arrangement has a number of problems. First, corrosion may develop between the surface of the magnet and the surface to be protected, i.e. at the interface. Such corrosion results in pitting of the surface to be protected. The electric conduction at the interface becomes inadequate and the attraction of the metal magnet relative to the surface may be considerably reduced. Although the sacrificial anode will continue supply protection, this sacrificial anode cannot sufficiently exert its influence in the area between the magnet and the surface to be protected. This corrosion may after some time be such that pit-corrosion occurs in one of the two interface surfaces, the pits becoming oxidized, so that the electric conduction becomes insufficient and the magnetic attraction is reduced. As a consequence, the object becomes “under-protected” and further corrosion occurs, which may grow to such an extent that the sacrificial anode and the metal magnet comes off the object and cathodic protection stops entirely.
As can be seen, there is a need for an improved sacrificial anode in a cathodic protection system, which does not exhibit undue corrosion at the interface between the sacrificial anode and the object to be protected. The cathodic protection system should have a better attachment method for connecting the sacrificial anode to the metal surface of the object, and it should be of a size that may be easily and commercially used for everyday objects used by a typical consumer, such objects being, for example, tractors, automobiles, tools, and the like.